pmacct: New addon

pmacct: New addon

- What is it?
   pmacct is a monitoring tool for network management tasks. Data collected
   can be used for analysis and troubleshooting purposes to maintain the
   health of the network. pmacct can collect, replicate and export network
   information. It can cache in memory tables, store persistently to SQLite3
   and output to flat-files like CSV, formatted, and JSON.
- Why is it needed?
   To monitor data usage (IP-based or MAC-based data accounting) down to the
   client level. Net-Traffic will monitor traffic for the entire RED, GREEN,
   etc. networks, but it cannot pinpoint which client is using lots of data.
   Connections will take a snapshot but not show day by day sums. pmacct can
   help admins keep tabs on users that use too much data.
- What are the use cases?
   An ISP may implement data caps and if the limit is over-run then you have
   to pay for every additional xxGB of data used. Typical charges can be
   around $10 per 50GB. With pmacct you can identify the high users and take
   action, hopefully before the limit is breached.
- This is being introduced as a command line only tool. However, at a later
   date, if it is useful to enough additional users a WUI page could be
   developed as discussed in the development mailing list
   https://lists.ipfire.org/pipermail/development/2021-January/009174.html
- Changes in V2 version
-   Initscript is using IPFire template and installed with IPFire method.
-   All other daemons except pmacct and pmacctd have been removed from the install.
-   Example conf files have been removed from /etc/pmacct
      Both example conf files are described in the pmacct wiki draft.

Tested-by:     Jon Murphy <jon.murphy@ipfire.org>
Signed-off-by: Jon Murphy <jon.murphy@ipfire.org>
Signed-off-by: Erik Kapfer <ummeegge@ipfire.org>
Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>